Mattress construction and plastic net spring bridging element for use therein

ABSTRACT

AN EXTRUDED PLASTIC NET, HAVING HEAVY STRANDS IN ONE DIRECTION AND LIGHTER STRANDS IN THE OTHER DIRECTION, IS USED TO REPLACE TWO PREVIOUS ELEMENTS I.E. (1) A WIRE-ROPE SPRING BRIDING UNIT, AND (2) A COTTOM SCRIM IN A MATTRESS CONSTRUCTION THUS PERMITTING SEWING OF THE SPRING BRIDGING UNIT TO THE CUSHIONING MATERIAL.

Feb. 16, 197i I R L. LARsEN 3,562,825

MATTRESS CONSTRUOTION AND PLASTIC NET SPRING BRIDGING ELEMENT FOR USETHEREIN Filed March 18, 1969 HIS ATTORNEY United States Patent Oflice3,562,825 Patented Feb. 16, 1971 MATTRESS CONSTRUCTION AND PLASTIC NETSPRING BRIDGING ELEMENT FOR USE THEREIN Ronald L. Larsen, Minneapolis,Minn., assignor to Conwed Corporation, St. Paul, Minn., a corporation ofDelaware Filed Mar. 18, 1969, Ser. No. 808,231 Int. Cl. A47c 23/30 US.Cl. -354 4 Claims ABSTRACT OF THE DISCLOSURE An extruded plastic net,having heavy strands in one direction and lighter strands in the otherdirection, is used to replace two previous elements i.e. (1) a wire-ropespring bridging unit, and (2) a cotton scrim in a mattress constructionthus permitting sewing of the spring bridging unit to the cushioningmaterial.

In present industrial practice it is common to provide a mattress with aspring foundation in which the springs are considerably spaced from eachother and then to provide a cushioning material thereover. In order toadequately support the cushioning material and to distributethe weightof the sleeping occupant over the springs it is also common to use aspring bridging unit comprising a wire and rope unit between the springfoundation and the cushioning material.

In such constructions it is common to provide the cushioning material(commonly a cotton batt) with a cotton scrim sewed to each face thereofto permit handling during manufacture and for other purposes.

It is not possible to stitch the wire and rope spring bridging elementto the cotton batt since the wire breaks the needles used in stitching.Accordingly, it i necessary to apply the wire and rope spring bridgingelement separately to the spring foundation.

One object of the invention is to reduce the number of parts in amattress construction by utilizing a single plastic net spring bridgingelement stitched to the cotton batt thus eliminating one of the twocotton scrims and the former wire and rope spring bridging element.

Another object of this invention is to simplify mattress construction byutilizing fewer materials.

Another object of this invention is to simplify the method ofmanufacturing mattresses by eliminating one of the steps required inmanufacture.

These and other objects of the invention will be apparent to thoseskilled in the art from the following specification and drawings inwhich:

FIG. 1 is a schematic showing of the assembly of a pad for mattresses,

FIG. 2 shows the plastic net spring bridging element of this invention,

FIG. 3 is a perspective view of the plastic net of FIG. 2, and

FIG. 4 is a cross section of a portion of a mattress constructionutilizing the spring bridging element of FIG. 2.

In the mattress construction industry one of the more common means ofconstructing a mattress is to first build a spring foundation of coilsprings tied together by wire ties of various kinds including,particularly, long coil springs wound across the outer coils of the mainsprings and attached at their ends to the wire border of the mattress. Awire and rope spring bridging element is then laid over the springfoundation. This wire and rope spring bridging element may be of theopen or of the woven variety. In the so-called open variety a pluralityof strands of twisted paper rope or other like cord are arrangedparallel on various spacings varying, for example, from 1 inch to 5inches or more on center. A plurality of Wire strands are arranged inthe opposite direction and passing through the twisted paper rope whichwire strands may vary similarly from 1 inch to 5 inches or more oncenter. In the woven variety of wire and rope spring bridging elementthe wire is shot through a layer of burlap. In either of these varietiesthe wire element or strands are typically a 19 gauge tempered steelwire.

Many manufacturers of such mattresses have their own equipment forconstructing cotton batts such as a carding machine, one variety ofwhich is referred to as a garnett machine. Such machines comb the cottonfibers into a loose batt which is then further provided with a cottonscrim on each side by sewing the scrim to the batt thus providing a morehandleable batt. In some manufacturing operations a topper comprising acushioning material to provide feel, such as a polyurethane foam, andthe outer ticking are also applied to one surface of the cotton battover the cotton scrim and sewed to the cotton batt as a unit at the sametime the two cotton scrims are provided. This latter method is commonlydone when a scroll pattern is desired on a deep quilted mattress. Whenthe upper layer of cushioning material and the ticking (frequentlycalled the topper) is not sewn as a unit to the cotton batt the samewill be separately sewed and applied.

The cotton batt, sewn together as above described, is then applied overthe wire and rope spring bridging unit and the topper (if notincorporated in the pad) is then applied and the mattress finished atthe borders.

The wire and rope spring bridging element is provided to distribute theweight of sleeping occupants and bridge the spaces Within and betweensprings and to provide a stiffness to the mattress. In some instancesthis wire and rope spring bridging element is used only at the center ofthe mattress due to its cost; however, it frequently covers the entiremattress, particularly in the better quality of mattress. In any event,it is necessary to cut the wire and rope spring bridging element from aroll to the appropriate size and to apply the same to the springfoundation and secure the same thereto as by hog rings or other knownmechanisms.

This invention is directed to a specific plastic net spring bridgingelement which not only replaces the wire and rope bridging element butalso replaces the sewable cotton scrim on one side of the cotton battwhen the mattress pad is formed. Thus one element of the previousconstruction is eliminated together with one of the steps ofmanufacture.

As shown in FIG. 1 the cotton batt portion 10 of the mattress pad isfirst formed in any suitable conventional forming means such as agarnett, indicated at 12. The cotton batt 10 is then conveyed to asuitable conventional stitching machine 14 which stitches through thebatt 10 by means of a gang of needles generally indicated at 16.

Also fed to the stitching machine 14 is a light cotton scrim 18 on thetop surface of the batt 10 and the sheet of plastic net 20. The cottonscrim 18 and the plastic net 20 may be fed from suitable rolls such asindicated at 22 and 24 respectively. The stitching machine 14 will thenstitch the cotton scrim 18 and the plastic net 20 to opposite faces ofthe cotton batt thus forming the mattress pad 26 which is rolled onto amandrel 28. If it is desired to combine the mattress pad 26 with thetopper in one operation suitable materials such as sheet polyurethanefoam may be fed from another roll 30 and the ticking or other coveringmay be fed from still an additional roll 32. Under such an arrangementthe topper materials including the ticking would be stitched to themattress pad in a single operaion.

The mattress pad 26 is then taken from the roll, cut to appropriatesize, and applied to the spring base. If the mattress pad 26 includesthe topper the entire construction is applied to the spring base orfoundation in one step whereas otherwise the topper must be separatelyapplied.

The plastic net of this invention is preferably an extruded plastic nethaving two sets of parallel strands with the strands of one set crossingthe strands of the other set at substantially a right angle. Such a netmay be readily extruded by use of the method and apparatus disclosed inUnited States Pat. No. 3,252,181. By use of the method and apparatus ofsaid patent considerable variation in the strand count, diameter ofstrands, and the like may be achieved. The particular construction ofthe net 20 of this invention, as shown in FIGS. 2 and 3, comprises aplurality of parallel strands 34 forming one set of strands and aplurality of strands 36 forming a second set of strands. The strands 36cross the strands 34 at substantially right angles thereto and integraljoints 38 are formed at the intersection of the strands 36 and 34 duringmanufacture. Preferably, the plastic net is oriented after extrusion byheating the same and stretching the same along the strands in onedirection while heated and then heating the same and stretching theother strands in their longitudinal direction and then cooling the netwhile so stretched. This tends to orient the molecular structure of thenet and provide a stronger net per unit of weight. In the specific net20 as shown in FIGS. 2 and 3, which is preferred, one set of strands 34are either not oriented or only oriented slightly while the strand 36are more highly oriented. With a proper combination of extrusion andorientation the strands 34 are provided having a considerably largersize in cross section than the strands 36. As seen in FIG. 3 strands 34are considerably larger than the strands 36. In one preferred embodimentthe heavy strands 34 have a diameter of 0.066" while the lighter strands36 have a diameter of 0.016". It must be understood, however, thatconsiderable variation in strand size may be tolerated by theconstruction and process of this invention and, additionally, thestrands do not necessarily have a circular cross section but may besomewhat elongated in cross section as shown for the strands 34 in FIG.3. The strands of greater orientation will tend to be more nearlycircular in cross section. In the preferred embodiment of the net 20 andafter orienting the extruded net the larger strands 34 are on 1 /2centers and the smaller strands 36 are on A centers. Such a constructionis excellent for use as a spring bridging element to firm the mattressand to bridge the space within and between coils in a construction suchas that shown in FIG. 4.

As shown in FIG. 4 the spring foundation 40 is made up from a pluralityof coil springs 42 tied together by long small coil springs 44 in knownmanner. The coil springs 44 are then fixed at their ends to the mattressborder 46, also in known manner. Over the spring foundation 40 themattress pad 26 is placed. As indicated above, the mattress pad 26comprises the central cotton batt 10, the scrim 18 and the net 20. Thethree elements (the cotton batt 10, the scrim 18 and the plastic net 20)are stitched together by stitches 48. Any topper (not shown) 4 notincorporated therewith during the stitching operation at the stitchingmachine 14. The mattress pad 26 is then fastened to the springfoundation 40 in any conventional manner.

A spring bridging element such as the previously used wire and rope mustbe capable of distributing the weight forces over the various springsacross the distances a between springs and across the spaces b withinthe top circular coil 43 of the coil springs 42. Previously, only theWire and rope bridging element adequately bridged between the springsand gave the adequate firmness to the mattress. Stiffness is required toadequately bridge the spaces a, b. Accordingly, the stiffer strands 34are arranged usually in the longer direction of the mattress to providebridging over more springs. It has been found, surprisingly, that theplastic net of the invention may be utilized in place of the extremelystrong wire and rope bridging element previously used, even though theplastic net of the invention is considerably less stiff and hasconsiderably less tensile strength as indicated by tests referred tobelow.

A sample of wire and rope having wires 0.95" on center and made up fromwires of 19 gauge tempered steel wire was tested for tensile strengthboth along the wire strand direction and transverse thereto. A plasticnet sample of this invention having a heavy strand 0.066" in diameterand a light strand 0.016" in diameter with the heavy strands on 1 /2"centers and the smaller strands on A" centers was also tested fortensile strength in each direction with the following results:

TABLE I (Tensile strength) Sample: Pounds per inch width Wire and rope(along length of wire strand) 280.0 Plastic net (along length of heavystrand) 16.0 Wire and rope (transverse to length of wire strand) 20.0Plastic net (along length of light strand) 21.5

Samples of the same two materials were then assembled over a springfoundation and use tested by a bouncing weight with the cycles of bouncereported for each sample tested. The two constructions gave thefollowing results:

TABLE II (Use test) Sample: Cycles Wire and rope assembly 1,800 cycles(wire broke).

Plastic net assembly 20,000 cycles (test stopped at 20,000 cycles-novisible deterioration).

It will be seen from the above table that the wire and rope and theplastic net have approximately the same tensile strength transverse tothe heavy strand (the wire strand of the wire and rope), and the wireand rope has a tensile strength 17 /2 times as great as the plastic netalong the bridging strands (the wire of the wire and rope and the heavystrand 34 of the plastic net). However, surprisingly, in actual use theplastic net gave 11 times the use.

Since stiffness is an important criterion in a spring bridging elementsince it relates to the ability to distribute the load and to thefirmness of the ultimate mattress, two samples like those used in TablesI and II were tested by a deflection test to determine the flexibilityalong the length of the bridging strand and transverse thereto. The testinvolved placing a 12" by 12" sample flat on a table with 6" overhangingthe edge of the table. The distance from the outer edge of the materialto the floor was then measured. Weights were added to the samples toachieve is then applied over the mattress pad 26 if the same is adeflection downwardly of at least 1". The distance from (Stiffness)Deflection 0.469 lbs/in.

Sample:

Wire and rope (wire direction) Plastic net (heavy strand direction)0.082 lbs/in. Wire and rope (transverse to wire direction) Deflectedunder its own weight. Plastic net (light strand direction) Deflectedunder its own weight.

Two samples of the same wire and rope and plastic net were constructedinto mattresses and found to have substantially equivalent firmness eventhough the wire and rope was from to 6 times as stiff as the plastic netas shown in Table III.

The preferred polymeric material for the plastic is a polypropylenealthough other extrudable plastic materials may be used.

It is not known exactly why the plastic net, which has considerably lesstensile strength and less stiffness should perform superior to the wireand rope when actually put together in the final construction asevidenced by the test results of Table II. Similarly, it is not knownexactly why the mattress should be equally as firm with either the wireand rope or with the plastic net even though the plastic net is muchless stifl than the wire and rope as indicated in Table III. While thereasons for these results are not known it is theorized that it is inpart due to the nature of the polymeric plastic of the net i.e.polypropylene which has a tendency to increase in strength when flexed.Also, the plastic net 20 as shown in FIG. 3 has the upper surfaces 35 ofthe strands 34 substantially flat and substantially co-planar with theupper substantially flat surfaces 37 of the strands 36. When the plasticnet 20 is stitched to the cotton batt 10 the net 20 is arranged with therelatively fiat co-planar surfaces 35, 37 of the strands 34, 36respectively adjacent to the cotton batt 10; it is believed, but notknown, that the substantially flat and substantially co-planar surfaces35, 37 provide a smoother and flatter support for the cotton batt 10than was previously the case with the wire and rope construction inwhich the wire and rope were of different diameters and in which thewire passed through the rope substantially centrally thereof. With thewire and rope the upper surfaces of the wire and the rope were atdifferent levels and as such tended to abrade the adjacent surface ofthe cotton batt 10.

In prior art constructions it was common to provide an insulatormaterial between the spring foundation and the wire and ropeconstruction in order to insulate against the clicking noise thatoccurred when the wire of the wire and rope bridging element clickedagainst the wires of the springs. Such insulating elements comprisedthin cotton batts or burlap or the like interposed between the wire andrope spring bridging element and the spring foundation. It has beenfound with the construction of this invention that not only does theplastic net eliminate the wire and rope spring bridging element and thecotton scrim previously sewed to the cotton batt, but also, the noiseinsulating element may be eliminated.

I claim:

1. A spring cushion structure comprising a resilient metal wire springfoundation presenting a face with open spaces between a plurality ofsmall wires in said face, said open spaces being large relative to saidwires, cushioning material supported by said face, an open mesh netinterposed between said face and said cushioning material, said nethaving a plurality of sets of polymeric plastic strands, strands of oneof said sets crossing strands of another set at an angle, the strands ofsaid one set being larger in cross section and stilfer than the strandsof the crossing set, strands of said one set bridging said open spacesbetween said small wires, the upper surfaces of strands of said one setbeing substantially co-planar with the upper surfaces of strands of saidcrossing set.

2. The spring cushion construction of claim 1 in which the crossing ofstrands of said one set with strands of the crossing set are jointsintegral with the strands forming the joints and in which the uppersurfaces of said integral joints are substantially co-planar with theupper surfaces of strands of said one set and with the upper surfaces ofstrands of said crossing set.

3. A spring bridging unit for bridging the spaces within and between thespring wires at the face of a spring foundation comprising an open meshnet material, said net having a plurality of sets of polymeric plasticstrands, strands of one of said sets crossing strands of another set atan angle, the strands of said one set being larger in cross section andstiffer than the strands of the crossing set, the crossings of strandsof said one set with strands of the crossing set being joints, saidjoints being integral with the strands forming said joints, and theupper surfaces of strands of said one set being substantially coplanarwith the upper surfaces of strands of said crossing set.

4. The spring bridging unit of claim 3 in which the upper surfaces ofsaid joints are substantially co-planar with the upper surfaces ofstrands of said one set and also with the upper surfaces of strands ofsaid crossing set.

References Cited UNITED STATES PATENTS 2,556,590 6/1951 Long 24960X2,649,899 8/ 1953 Williams 5354 3,087,171 4/1963 Hoagland 5--3543,315,283 4/1967 Larsen 5354 BOBBY R. GAY, Primary Examiner A. M.CALVERT, Assistant Examiner US. Cl. X.R. 5-351; 297-452

